Auto Parts Cheaper Blog

2005-2007 Ford Mustang Smart Junction Fuse Box Problems Symptoms and Cures Including Schematics.

The Original Problem

Do you have a 2005-2007  Mustang. Do you have annoying electrical problems that are driving you crazy?

Get your new Smart Junction box here 

Although each Mustang is different and can either show just one or many of these symptoms, the list below is the most common, symptoms we know of, but does not describe every symptom. The only way to know if your SJB is bad with 100% Accuracy is to have it tested by a qualified mechanic with the proper equipment.


The SJB is on the passenger Kick Panel


Note: All Smart Junction Boxes new or used must be programmed to your individual mustang to work properly.


Common Symptoms of a bad SJB. (this is a broad range of symptoms, your vehicle may only experience one or more symptoms at a time).

  • One or More Brake lights is stuck on at all time.
  • Battery Drains Quickly When Car Sits for a few days
  • Headlights are on bright all the time.
  • Turn Signals or parking lights are stuck.
  • Power Windows do not work
  • Instrument cluster malfunctions
  • Dash lights quit working.


The original Smart Junction Box installed in these Mustangs had 2 major problems.

Problem 1: The windshield leak problem. These cars had a bad seal from the factory that allowed rain to drip down on the bottom of the windshield. The water leaks directly into the SJB box, and ruins it.

Problem 2: Poorly engineered part when the car was new. These circuit boards were poorly made, and after a few years of heat and cold, they fail to function any more. There are no repairable parts in a SJB; the whole module must be replaced.


Get your new Smart Junction box here 


Normal Operation

The smart junction box (SJB) sends reference signals to the headlamp switch through circuits 1400 (TN/WH), 1401 (BK/LG), and 1402 (RD/WH). At any given time, the headlamp switch routes one of the input circuits to ground through circuit 1205 (BK).


When the SJB detects the headlamp switch in the HEADLAMPS ON position and the multifunction switch in the LOW BEAM position, the SJB sends voltage through circuit 1338 (WH) and circuit 1336 (LG/WH) to the LH and RH low beams, respectively.


The SJB sends a reference signal to the multifunction switch through circuits 1394 (WH/RD) and 1395 (RD/PK). When the multifunction switch is placed in the FLASH

-TO-PASS or HIGH BEAM position, the voltage signal is routed back to ground, internal to the SJB. When the SJB detects a request for flash-to-pass or high beams, the SJB provides ground to the high beam relay through circuit 1708 (LG/BK). When the high beam relay is energized, voltage is provided through circuits 1337 (VT/YE) and 1335 (YE/WH) to the LH and RH high beams, respectively.

Possible Causes

  • Circuit 1205 (BK) open
  • Circuit 1335 (YE/WH) short to voltage
  • Circuit 1336 (LG/WH) short to voltage
  • Circuit 1337 (VT/YE) short to voltage
  • Circuit 1338 (WH) short to voltage
  • Circuit 1394 (WH/RD) short to ground
  • Circuit 1395 (RD/PK) short to ground
  • Circuit 1400 (TN/WH) open
  • Circuit 1401 (BK/LG) open
  • Circuit 1402 (RD/WH) short to ground
  • Circuit 1708 (LG/BK) short to ground
  • High beam relay
  • Headlamp switch
  • Multifunction switch
  • BEC (Bussed Electrical Center)
  • SJB (Smart Junction Box)


sjb2 sjb3


Get your new Smart Junction box here 

8 Responses to “2005-2007 Ford Mustang Smart Junction Fuse Box Problems Symptoms and Cures Including Schematics.”

  1. google says:

    A site that isn’t indexed much by Google or doesn’t turn up until page 1,993,
    990 on a Google search for its kind is WORTHLESS to you.
    They might keep visiting it over and over or a
    lot of them might mention it to their friends and relatives.
    The number of followers, delivery time and rates are three components which vary from one plsn to another.

  2. Cecilia says:

    You share interesting things here. I think that your blog can go viral easily, but you
    must give it initial boost and i know how to do it, just search in google – omgerido trafic method

  3. Your web site emerged inside my search and i’m in awe of what you have published on this topic. I am currently expanding my inquiry and thus cannot contribute further, nevertheless, I’ve got bookmarked your site and will be going back to stay informed about any upcoming updates. Really love it and gives appreciate your tolerating my comment.

  4. Hermine says:

    How many of you need extra cash ? Today i quit my regular
    job, now i earn online, you can earn too.
    One month ago i was searching internet for money making ideas and found interesting roulette system.
    I gave it a try and now make 70 £ a day. If you want more info
    just type in google – platinum roulette system

  5. It has increased its popularity due to the demand and the need for people to look better and improve their current physical state. With this reason, it is now a billion dollar industry.

  6. diwali deals says:

    This kind of is among the actual advisable domain I have ever ever possible visitied. the information is take a moment to extraordinary.

  7. Kanye west says:

    Do you mind if I quote a few of your articles as long as I provide credit and sources
    back to your site? My website is in the exact same area of interest
    as yours and my users would really benefit from some of the information you present here.
    Please let me know if this okay with you. Appreciate it!

  8. I truly appreciate this post.Really looking forward to read more. Really Great.

Leave a Reply